Shear-wave velocity structure beneath the Ngauruhoe Volcano, New Zealand using receiver function inversion with the genetic algorithm

Abstract:

The Ngauruhoe Volcano is an andesitic volcano of 2,291 m height in the North Island, New Zealand. One-dimensional shear-wave velocity (Vs) structure beneath the OTVZ seismic station near the volcano was inferred by the genetic algorithm (GA) inversion of radial receiver functions (RFs). Radial RFs were derived from 337 teleseismic events (M_w ≥ 5.5 and epicentral distances between 30° and 90°) recorded by a broad-band seismometer at the seismic station during the period from November 11, 2011 to September 11, 2013. Among the derived RFs, only 87 RFs with higher signal to noise ratios were used for the GA inversion method. Three hundred velocity models for 100 generations were derived using velocity models comprising 32 layers with a maximum depth of 60 km. The inverted models were averaged to obtain the final Vs model, which indicates a clear discontinuity at a depth of 18±1 km where Vs abruptly increases from 3.1 to 4.0 km/s. Above the sharp Vs discontinuity indicating the Moho, an average Vs is 2.8 km/s. Low-velocity layers (LVLs) are identified at depths of 10-16 km in the lower crust (Vs < 3.0 km/s) and 28-40 km in the upper mantle (Vs < 4.4 km/s). Corresponding average Vs are 2.8 and 4.2 km/s, respectively. The thin crust with relatively low velocities and existence of LVLs in the lower crust and upper mantle allude to the presence of magma associated with the subducting Pacific Plate. The limited number of teleseismic events recorded at the OTVZ station prevents from further investigation into the effect of RFs of dipping boundaries and anisotropy.